diff --git a/themes/tiddlywiki/snowwhite/base.tid b/themes/tiddlywiki/snowwhite/base.tid
index 81c402b13..e42794298 100644
--- a/themes/tiddlywiki/snowwhite/base.tid
+++ b/themes/tiddlywiki/snowwhite/base.tid
@@ -706,12 +706,7 @@ canvas.tw-edit-bitmapeditor  {
 }
 
 .modal {
-	position: fixed;
-	top: 50%;
-	left: 50%;
 	z-index: 1100;
-	width: 560px;
-	margin: -250px 0 0 -280px;
 	background-color: #fff;
 	border: 1px solid #999;
 	border: 1px solid rgba(0,0,0,.3);
@@ -719,6 +714,34 @@ canvas.tw-edit-bitmapeditor  {
 	<<box-shadow "0 3px 7px rgba(0,0,0,0.3)">>
 }
 
+@media (max-width: 55em) {
+
+.modal {
+	position: absolute;
+	top: 1em;
+	left: 1em;
+	right: 1em;
+}
+
+.modal-body {
+	overflow-y: auto;
+	max-height: 400px;
+}
+
+}
+
+@media (min-width: 55em) {
+
+.modal {
+	position: fixed;
+	top: 50%;
+	left: 50%;
+	width: 560px;
+	margin: -250px 0 0 -280px;
+}
+
+}
+
 .modal-header {
 	padding: 9px 15px;
 	border-bottom: 1px solid #eee;
@@ -730,8 +753,6 @@ canvas.tw-edit-bitmapeditor  {
 }
 
 .modal-body {
-	overflow-y: auto;
-	max-height: 400px;
 	padding: 15px;
 }